Can you confirm that the good point of asking payment for service ...
If your "service" violates PayPal's Acceptable Use Policy (which you can view from the Legal Agreements link at the bottom of any PayPal page), buyers can dispute a payment, and they will probably win. Your PayPal account will be quickly terminated.
If your service is allowed by PayPal's Acceptable Use Policy, buyers are not covered by PayPal Buyer Protection for a "service". They can dispute the charge, but will probably lose if they escalate it to a "claim".
If you are not providing a service, but are using the term "service" to avoid disputes, you will probably lose a dispute.
If the payment was made via a credit card, buyers still have full protection afforded them by Visa/MC/AmEx. If they do a credit card "chargeback", PayPal's hands are tied, and Visa/MC/AmEx is the final arbitrator of the payment. they tend to favor their cardholders in a dispute.
If you lose a chargeback from Visa/MC/AmEx, and PayPal refunds their money, you still have the court system, and can file a small-claim against the buyer.